Method for the heating of material or the performance of chemical processes in electrical furnaces, together with apparatus intended therefor



\ T. A. F. HOLMGREN AND C. T. THORSELL. METHOD FOR THE HEATING 0F MATERIAL OR THE PERFORMANQE OF CHEMICAL PROCESSES IN ELECTRICAL FURNACES, TOGETHER WITH APPARATUS INTENDED THEREFOR.

APPLICATION FILED JULY 24,1919- 1,342,809. Patented June 8, 1920.

ITTOR/VE y UNITED STATES PATENT OFFICE.

TORSTEN ANDREAS FRITHIOFSSON HOLMG-REN, OF STOCKHOLM, AND CARL THEODOR THORSELL, 0F GOTTENBORG, SWEDEN, ASSIGNORS TO AKTIEBOLAGET KVOFVEIN- DUSTRI, OF GOTTENBORG, SWEDEN, A LIMITED COMPANY.

METHOD FOR THE HEATING OF MATERIAL OR THE-PERFORMANCE OF CHEMICAL PROCESSES IN ELECTRICAL FURNACES, TOGETHER WITH APPARATUS INTENDED THEREFOR.

Specification of Letters Patent,

Patented June 8, 1920.

' Application and m 24, 1919. Serial No. 313,048.

To all whom it may concern:

Be'it known that we, TORSTEN ANDREAS FRITHIOFSSON HOLMGREN, chief engineer, sub'ect of the King of Sweden, and resident of ngelb'rektsgatan 14, Stockholm in the Kingdom of Sweden, and CARL HEODOR T HonsELL, engineer, subject of'the King of Sweden, and resident of Kopmangatan 20, Gottenborg, in the Kingdom of Sweden, have invented certain new and'useful improvements in methods for the heating of material or the performance of chemical processes in electrical furnaces, together with apparatus intended therefor, as set forth in the annexed specification.

In electrical resistance furnaces, z. e. furnaces in which the mass or the material to be heated, itself forms the resistance for the electric current by means of which the heating is generated, forv example furnaces intended for chemical processes, it has been found that in cases where the material to be heated is of such a nature that the electric resistance in it is decreasing as the temperature rises, a uniform heatingis very difiicult to attain. This is the case with secondolass conductors, metal oxids, cement, and the like. Ifv such a mass is heated. for example to 1000", the electric resistance of the mass is vastly less than, for example, at 800, which has the result that the inten sity of current between the electrodes increases at the points or in the paths of the current where the temperature is highest,

whereby intensely heated paths for the current are formed in the mass, whereas the latter, especially if it is a bad conductor of heat, may elsewhere remain relatively cool. This phenomenon renders impossible or difficult, in the case of various materials, a uniform heating bymeans of an electric current which passes through the mass between two electrodes, or groups of electrodes.

In order to eliminate this difliculty, the heating, in accordancewith the present invention, is generated by means of two different electric circuits of single-phase alternating current, the current being supplied to the mass intended for the heating and serving as a resistance by two pairs of electrodes or two pairs of groups of electrodes'suitably arranged for the purpose, 1I l such a manner that the current in one circuit is 90, or approximately 90, out of phase with the current in the other circuit.

Consequently the two currents combine in the furnace in such a manner that the temperature of the mass between the four electrodes or the four groups of electrodes is equalized, so that instead of a comparatively narrow (limited) current path being formed in the mass, a widening of the cur rent path is effected, and thereby also an expansion of the heating zone in the mass to be heated. H

In order to make plain the invention, there is shown on the appended drawing, as an example, diagrammatically, two different forms of a device suitable for the purpose. Figure 1 shows diagrammatically in horizontal section the invention as applied to a shaft furnace octagonalin cross section, in which it is assumed that two single-phase alternating currents with, a

phase-displacement of 90 are used with the same current and tension in the two phases. In Fig. 2 the invention is shown as applied to. a furnace chamber rectangular in cross section, the current being drawn from a. three-phase transformer.

Fig. 3 shows 1n vertical section a shaft furnace arranged in accordance with the present inventlon, with the lower part not shown. Fig. 4 shows a horizontal section of the same along the line I-I in Fig. 3.

The invention is described first with reference to Fig. 1. 1 designates the shaft proper, which is provided with two pairs of electrodes A, A, B, B, arranged in the walls of the shaft in such a way that straight lines between the opposite electrodes form an angle of 90 to one another. The shaft or heating-room is provided with suitable charging and discharging arrangements for the introduction of the material to be treated and the discharge of the product, respectively.

If current were to be sup lied only through the two electrodes A, opposite to one another, this would have the result that the mass between the electrodes would be gradually heated, whence, under the assumption stated above, the conductivity of the heated portion of the mass would be increased, and the current would accordingly concentrate itself at the hottest parts, whereby their conductivity would be still further augmented, 2'. e. such a reaction between the increase in the heating of the material and in its conductivity would ensue that the transmission of the current, and therewith also the heating of the material wou d be concentrated on a very limited channellike part of the mass between the electrodes A, A, especially if the mass is a bad conductor of heat.

If instead of using merely one singlephase alternating current between the electrodes AA, there is introduced into the furnace between the electrodes BB another single-phase alternating current from a transformer winding electrically separated from the circuit" of the first-mew tioned alternating current, and this latter alternating current is so selected that it differs in phase by 90 from the first-mentioned alternating current, the two currents act in the furnace in such a manner that the temperature in the mass between the four electrodes is equalized. The process is described as follows: The tension-drop along the current introduced between the electrodes -BB per unit length of current path will be least in the parts of the mass where the temperature is highest, and hence the resistance least. The development of energy in the current path B-B' will thus be greatest in the parts of the mass where the temperature is lowest, and it thus strives to equalize the temperature in the layer of the mass which is between the two pairs of electrodes.

If the path taken by the current in the mass between the four electrodes is examined, it will be found that the fact that two-phase alternating current has been chosen compels the resulting current which is suipplied through the electrodes A-A and B during the course of each entire period to travel first from e. g. the stretch AB-A to the position A-A, or 13-13 respectively, and finally to return to AA and A''B-A or B-l3 respectively. The current will in this manner be forced into a disk-like expansion in the heating-chamber between the electrodes.

In Fig. 1, the reference numerals 2 and 3 designate the two phases of a twophase alternating current with the same strength and the same tension in the two phases, which nevertheless, as indicated above, are displaced 90 out of phase in relation to one another, whereas the two electrode pairs are so arranged that straight lines between opposite electrodes also form an angle of 90 or practically 90.

It should be obvious that each electrode called zero electrode in the furnace.

pass through the heating zone formed between the electrodes.

It is further evident that the transformer windings 2 and 3 may be connected with oneanother at a neutral point, which should then preferably be placed in the center of the coils and which, if desired, may be connected to earth or connected with a so- B such connection the two one-phase alter nating current circuits will be combined into what is usually called a two-phase systerm or a four-phase system. Even without this connection they may also be regarded as together forming a two-phase system.

The invention can naturally be applied also to furnaces constructed in other ways.

In Fig. 2 the invention is shown as applied to a furnace chamben with rectangular section with the use of a three-phase transformer as a source for the current, the two phases 4, 5 being connected to the electrodes A, A opposite to one another, whereas the third phase 6 is connected to the two--elec- -trodes B, B, which are arranged in such a manner that a straight line between them forms an angle of approximately 90 with a straight line between the two other electrodes A, A.

It should be manifested from the above that the tension between the electrodes B, B is at right angles to the tension between the electrodes A, A. The invention has been described above with reference to the use of merely two current circuits, which differ 90 or approximately 90 in phase from one another, whereas the corresponding electrodes are arranged in such a manner that the lines of junction between the electrodes belonging to each current circuit form an equal angle to one another.

The invention can naturally also be applied with the use of-more than two current circuits, for example 3 current circuits, in which case the different current circuits are displaced 60 out of phase with one another,

' appreciable currents one another in the same furnace for the supply of the energy which is required. not merely for the actual heating of the material, but also for the production 0 the desired reaction inthe furnace.

As a general rule, however, it is most suitable to place these heating places, which are series connected with one another, above shaft. This, however, gives rise to currents in a vertical direction. If several heating zones situated above one another are required in the same shaft or furnace chamber without between the different zones, this is attained simply by the fact that thepairs of electrodes in each such zone are fed each from its transformer coil. Such a furnace is shown in Figs. 3 and 4:.

The furnace shaft is composed of an outer covering 7 of bricks and an inner lining 8,

suitably of chamotte bricks. The space between these is filled by a heat insulating mass 19, such as infusorial earth (kieselguhr). According'to the form illustrated in the drawing, the upper part of the shaft in horizontal section has inwardly an octagonal shape, whereas its lower expanded part 9 is of quadratic horizontal section.

A, A, B, B designate the .electrodes, which are in electric connection with carbon rods, or the like, serving for the supply of the current. According to the form shown in Figs. 3 and 4, there are two sets of electrodes arranged above one another, the one set passes through the walls in the upper part of the furnace, whereas the other series of electrodes passes into the furnace shaft at the point of transition between the upper octagonal and the lower rectangular part of the shaft.

Obviously also more than two sets of electrodes can be arranged aboveone another, or succeeding one another, in the direction in which the charge is through the furnace.

12 designates iron beams serving for the support of the shaft. The lower part (not shown) of the furnace 1s provided with dis-.

charge arrangements, constructed in some suitable manner with reference to the prod uct which it is desired to manufacture.

Having thus described our invention, we declare, that what we claim is 1. Method for heating of material in electric resistance furnaces, for example for the performance of chemical reactions, characterized by the fact that the heating is produced by means of alternating current which is supplied by two or more current circuits which in regard to phase are displaced in relation to one another at an angle which is equal, or approximately equal, to 180 or 360, divided by the number of current circuits.

. former, or groups of of which fed forward a approximately 90.

3. Method as stated in claim 1 characterized by the fact that the heating is produced in several heating zones situated above or in sequence to one another, looking in the direction of movement of the material 4. Apparatus method as stated in claim 1 characterized by the fact that the pairs of electrodes arranged in the furnace in a suitable manner for the purpose are connected each to its phase of a two-phase generator or transgenerators or transformers (Fig. 1), besides which the electrodes are so arranged that the separate paths of current between the opposite electrodes in the two pairs of electrodes form --an angle of 90 or approximately 90 to one another.

5. Apparatus method as stated in clalms 1 and 2, characterized by the fact that the electrodes pairs arranged in the furnace in some manner.suitable for the purpose are connected to .a three-phase transformer in such a manner that one of the pairs of electrodes is connected to two phases, while the other pair is connected to the third phase, besides which the electrodes are so arranged that straight lines between 'the opposite electrodes in the two pairs of electrodes form an angle of 90 or approximately 90 to one another.

6. Method as ized by the fact that the heating 15 produced in several heating zones situated in sequence to one another, looking in the direction of movement of the material.

7 Apparatus for the, performance of the method as stated in claim 2, characterized by the fact that the pairs of electrodes arranged in the furnace in a suitable manner for the purpose are connected each to its phase of a two-phase generator, beside which the electrodes are so arranged. that the separate paths of current between the opposite electrodes in the two pairs of electrodes form an angle of approximately 90 to one another. i

for the performance of the for the performance of the stated in claim 2, character- In witness whereeof we have hereunto set 

